In the state of the art, welded tube shafts are known that are constructed of two endpieces each welded to one and of a hollow tube. Each endpiece comprises a first portion provided with connection fluting such as splines. The splines are adapted to connect the shaft, for example to a correspondingly splined inner joint part of a constant velocity joint. Each endpiece has a tubular second portion that is welded to the hollow tube. The second portion has an inner surface that is cylindrical and an end-wall surface that is substantially flat. The cylindrical inner surface is connected to the end-wall surface via a surface forming a portion of a torus.
During fabrication, the endpieces of known welded tube shafts are subjected to normalization annealing which leads to local decarburization of the endpiece at the location of the surface in the form of a portion of a torus.
Furthermore, after welding, the welded tube shaft is subjected to induction heat-treatment that creates a heat-treated zone in the outer portion of the shaft and a zone that is not heat-treated situated inside the endpieces, with the two zones being separated by a line of separation. Usually, the line of separation is terminated at the surface in the form of a portion of a torus.
Because of those various fabrication parameters, the structural stability and the service lifetime of the known shaft are compromised.